.left-ad{
  position: fixed;
  bottom: 2%;
  left: 14px;
  z-index: 9999;
}
.left-ad-img1 , .left-ad-img2{
  float: left;
  cursor: pointer;
}
.left-ad-img2{
  display: none;
}
.left-ad:hover .left-ad-img2{
  display: block;
}